Positron emission tomographic (PET) studies of brain aging in rhesus macaques (Macaca mulatta) are aimed at extending the primate model of brain aging, and evaluating the efficacy and survivability of nerve growth factor (NGF) grafts in vivo. The major goals of these studies are to evaluate cerebral glucose metabolism in behaviorally characterized monkeys, and to determine if PET can be used to monitor the neurobiological and behavioral changes produced by NGF grafts. Studies of the survivability and efficacy of NGF grafts are important because NGF grafts are a potential treatment for neurodegenerative disorders, such as Alzheimer's disease. Earlier reports of similar age-related changes in human and nonhuman primates, including memory impairments, regional cell loss, amyloid plaque formation, and neurochemical changes, support the use of macaques as a model of human brain aging. Initial PET studies in aged and young animals have shown deficits in cerebral glucose metabolism in monkeys that are similar to those observed in humans, further supporting the use of this model. The use of PET and the metabolic tracer 2-(18F)-fluoro-deoxyglucose (FDG) to evaluate NGF grafts in vivo will permit longitudinal studies and enable the evaluation of the relationship between changes in regional cerebral glucose metabolism and behavior. Thus far, we have studied a group of animals before and after the implantation of NGF or control grafts. While these data have not yet been fully analyzed, we have found a relationship between glucose metabolism in the frontal lobes and performance on a behavioral task at baseline. these results show that animals with impaired performance on a delayed response task had lower metabolic rates in the orbitofrontal cortex than unimpaired animals. Further analysis of these data will evaluate the relationship between NGFG grafts, behavioral performance and glucose metabolism.